1. Field of the Invention
The present invention relates to a constant velocity joint used in power transmission shafts for automobiles and the like and particularly it relates to a constant velocity joint which makes it possible to effect angular displacement and axial displacement between a driving shaft and a driven shaft.
2. Prior Art
This type of constant velocity joint, as shown in FIG. 3, comprises a hollow outer member 3 having a cylindrical hole 2 formed with straight guide grooves 1 parallel with the axis, an inner member 6 having a part-spherical outer surface 5 formed with straight guide grooves 4 parallel with the axis cooperating with the grooves 1 to define ball tracks, torque transmitting balls 7 disposed in the grooves 1 and 4, and a cage 11 having ball pockets 8 for receiving the balls 7 and also having part-spherical inner surface 9 and part-spherical outer surface 10 respectively contact-wise guided by the part-spherical outer surface 5 of the inner member 6 and by the cylindrical hole 2 of the outer member 3 and having centers of curvature shifted axially of the joint on the opposite sides of the ball center plane.
When a crossing angle between the outer member 3 and the inner member 6 is given, and when the joint is located with a torque while axially sliding, the cage 11 functions to retain the torque transmitting balls 7 in the bisecting plane of the crossing angle. The members are lubricated as by grease in view of relative slippage taking place therebetween.
There is a constant velocity joint of this type shown in FIG. 4, wherein the slide resistance of the joint is reduced to allow smooth axial displacement with angular displacement between the outer member 3 and the inner member 6 (see Japanese Utility Model Publication No. 63-2665).
In this constant velocity joint, the inner surface 9 of the cage 11 comprises a cylindrical surface 9a in an axially middle region, and spherical surfaces 9b disposed on the opposite sides thereof, the radius of curvature Rc of the spherical surfaces 9b being seemingly the same as the radius of curvature Ri of the outer surface 5 of the inner member 6. The center of curvature O.sub.4 of the outer surface 10 of the cage 11 is axially shifted with respect to the ball center plane P, while the axial center O.sub.3 of the inner surface 9 is axially shifted from the ball center plane P by the equal distance in the opposite direction of O.sub.4. The centers of curvature O.sub.1 and O.sub.2 of the spherical surfaces 9b are axially and equally spaced from the O.sub.3 on the opposite sides thereof, whereby an axial clearance is defined between the inner surface 9 of the cage 11 and the outer surface 5 of the inner member 6. In addition, in this figure, the center of curvature of the outer surface 5 of the inner member 6 is shown in axial relative positional relation, coinciding with O.sub.3. And there is a slight pocket clearance (5-50 .mu.m) between the torque transmitting ball 7 and the ball pocket 8, which, in this constant velocity joint, coupled with the construction allowing a relative axial short travel of the inner member 6 and the cage 11, enables the ball 7 to roll smoothly, achieving a reduction in the axial slide resistance of the joint.
The constant velocity joint described above is superior in that it ensures smooth rolling of balls and reduction in axial slide resistance of the joint. On the other hand, however, there is still much room for improvement in connection with the interior slide resistance between the members. More particularly, the cage 11 is constructed so that the radius of curvature Rc of the arc 9b of the inner surface 9 is seemingly equal to the radius of curvature Ri of the outer surface 5 of the inner member 6; therefore, when the inner surface 9 of the cage 11 and the outer surface 5 of the inner member 6 come in contact with each other while the cage 11 and the inner member 6 are axially moving relative to each other while making angular displacement owing to scatter in manufacturing tolerance, there occur a variation in slide resistance in the contact region due to the changing contact position and a variation in slide resistance due to time-dependent change. Thus, it has been found that there is much room for improvement so as to reduce the slide resistance of the joint.